<!doctype html>
<html>
<head>
<meta charset='UTF-8'><meta name='viewport' content='width=device-width initial-scale=1'>

<link href='https://fonts.loli.net/css?family=Open+Sans:400italic,700italic,700,400&subset=latin,latin-ext' rel='stylesheet' type='text/css' /><style type='text/css'>html {overflow-x: initial !important;}:root { --bg-color:#ffffff; --text-color:#333333; --select-text-bg-color:#B5D6FC; --select-text-font-color:auto; --monospace:"Lucida Console",Consolas,"Courier",monospace; --title-bar-height:20px; }
.mac-os-11 { --title-bar-height:28px; }
html { font-size: 14px; background-color: var(--bg-color); color: var(--text-color); font-family: "Helvetica Neue", Helvetica, Arial, sans-serif; -webkit-font-smoothing: antialiased; }
body { margin: 0px; padding: 0px; height: auto; inset: 0px; font-size: 1rem; line-height: 1.42857; overflow-x: hidden; background: inherit; tab-size: 4; }
iframe { margin: auto; }
a.url { word-break: break-all; }
a:active, a:hover { outline: 0px; }
.in-text-selection, ::selection { text-shadow: none; background: var(--select-text-bg-color); color: var(--select-text-font-color); }
#write { margin: 0px auto; height: auto; width: inherit; word-break: normal; overflow-wrap: break-word; position: relative; white-space: normal; overflow-x: visible; padding-top: 36px; }
#write.first-line-indent p { text-indent: 2em; }
#write.first-line-indent li p, #write.first-line-indent p * { text-indent: 0px; }
#write.first-line-indent li { margin-left: 2em; }
.for-image #write { padding-left: 8px; padding-right: 8px; }
body.typora-export { padding-left: 30px; padding-right: 30px; }
.typora-export .footnote-line, .typora-export li, .typora-export p { white-space: pre-wrap; }
.typora-export .task-list-item input { pointer-events: none; }
@media screen and (max-width: 500px) {
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  #write { padding-left: 20px; padding-right: 20px; }
}
#write li > figure:last-child { margin-bottom: 0.5rem; }
#write ol, #write ul { position: relative; }
img { max-width: 100%; vertical-align: middle; image-orientation: from-image; }
button, input, select, textarea { color: inherit; font: inherit; }
input[type="checkbox"], input[type="radio"] { line-height: normal; padding: 0px; }
*, ::after, ::before { box-sizing: border-box; }
#write h1, #write h2, #write h3, #write h4, #write h5, #write h6, #write p, #write pre { width: inherit; }
#write h1, #write h2, #write h3, #write h4, #write h5, #write h6, #write p { position: relative; }
p { line-height: inherit; }
h1, h2, h3, h4, h5, h6 { break-after: avoid-page; break-inside: avoid; orphans: 4; }
p { orphans: 4; }
h1 { font-size: 2rem; }
h2 { font-size: 1.8rem; }
h3 { font-size: 1.6rem; }
h4 { font-size: 1.4rem; }
h5 { font-size: 1.2rem; }
h6 { font-size: 1rem; }
.md-math-block, .md-rawblock, h1, h2, h3, h4, h5, h6, p { margin-top: 1rem; margin-bottom: 1rem; }
.hidden { display: none; }
.md-blockmeta { color: rgb(204, 204, 204); font-weight: 700; font-style: italic; }
a { cursor: pointer; }
sup.md-footnote { padding: 2px 4px; background-color: rgba(238, 238, 238, 0.7); color: rgb(85, 85, 85); border-radius: 4px; cursor: pointer; }
sup.md-footnote a, sup.md-footnote a:hover { color: inherit; text-transform: inherit; text-decoration: inherit; }
#write input[type="checkbox"] { cursor: pointer; width: inherit; height: inherit; }
figure { overflow-x: auto; margin: 1.2em 0px; max-width: calc(100% + 16px); padding: 0px; }
figure > table { margin: 0px; }
thead, tr { break-inside: avoid; break-after: auto; }
thead { display: table-header-group; }
table { border-collapse: collapse; border-spacing: 0px; width: 100%; overflow: auto; break-inside: auto; text-align: left; }
table.md-table td { min-width: 32px; }
.CodeMirror-gutters { border-right: 0px; background-color: inherit; }
.CodeMirror-linenumber { user-select: none; }
.CodeMirror { text-align: left; }
.CodeMirror-placeholder { opacity: 0.3; }
.CodeMirror pre { padding: 0px 4px; }
.CodeMirror-lines { padding: 0px; }
div.hr:focus { cursor: none; }
#write pre { white-space: pre-wrap; }
#write.fences-no-line-wrapping pre { white-space: pre; }
#write pre.ty-contain-cm { white-space: normal; }
.CodeMirror-gutters { margin-right: 4px; }
.md-fences { font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; overflow: visible; white-space: pre; background: inherit; position: relative !important; }
.md-fences-adv-panel { width: 100%; margin-top: 10px; text-align: center; padding-top: 0px; padding-bottom: 8px; overflow-x: auto; }
#write .md-fences.mock-cm { white-space: pre-wrap; }
.md-fences.md-fences-with-lineno { padding-left: 0px; }
#write.fences-no-line-wrapping .md-fences.mock-cm { white-space: pre; overflow-x: auto; }
.md-fences.mock-cm.md-fences-with-lineno { padding-left: 8px; }
.CodeMirror-line, twitterwidget { break-inside: avoid; }
svg { break-inside: avoid; }
.footnotes { opacity: 0.8; font-size: 0.9rem; margin-top: 1em; margin-bottom: 1em; }
.footnotes + .footnotes { margin-top: 0px; }
.md-reset { margin: 0px; padding: 0px; border: 0px; outline: 0px; vertical-align: top; background: 0px 0px; text-decoration: none; text-shadow: none; float: none; position: static; width: auto; height: auto; white-space: nowrap; cursor: inherit; -webkit-tap-highlight-color: transparent; line-height: normal; font-weight: 400; text-align: left; box-sizing: content-box; direction: ltr; }
li div { padding-top: 0px; }
blockquote { margin: 1rem 0px; }
li .mathjax-block, li p { margin: 0.5rem 0px; }
li blockquote { margin: 1rem 0px; }
li { margin: 0px; position: relative; }
blockquote > :last-child { margin-bottom: 0px; }
blockquote > :first-child, li > :first-child { margin-top: 0px; }
.footnotes-area { color: rgb(136, 136, 136); margin-top: 0.714rem; padding-bottom: 0.143rem; white-space: normal; }
#write .footnote-line { white-space: pre-wrap; }
@media print {
  body, html { border: 1px solid transparent; height: 99%; break-after: avoid; break-before: avoid; font-variant-ligatures: no-common-ligatures; }
  #write { margin-top: 0px; padding-top: 0px; border-color: transparent !important; padding-bottom: 0px !important; }
  .typora-export * { -webkit-print-color-adjust: exact; }
  .typora-export #write { break-after: avoid; }
  .typora-export #write::after { height: 0px; }
  .is-mac table { break-inside: avoid; }
  .typora-export-show-outline .typora-export-sidebar { display: none; }
}
.footnote-line { margin-top: 0.714em; font-size: 0.7em; }
a img, img a { cursor: pointer; }
pre.md-meta-block { font-size: 0.8rem; min-height: 0.8rem; white-space: pre-wrap; background: rgb(204, 204, 204); display: block; overflow-x: hidden; }
p > .md-image:only-child:not(.md-img-error) img, p > img:only-child { display: block; margin: auto; }
#write.first-line-indent p > .md-image:only-child:not(.md-img-error) img { left: -2em; position: relative; }
p > .md-image:only-child { display: inline-block; width: 100%; }
#write .MathJax_Display { margin: 0.8em 0px 0px; }
.md-math-block { width: 100%; }
.md-math-block:not(:empty)::after { display: none; }
.MathJax_ref { fill: currentcolor; }
[contenteditable="true"]:active, [contenteditable="true"]:focus, [contenteditable="false"]:active, [contenteditable="false"]:focus { outline: 0px; box-shadow: none; }
.md-task-list-item { position: relative; list-style-type: none; }
.task-list-item.md-task-list-item { padding-left: 0px; }
.md-task-list-item > input { position: absolute; top: 0px; left: 0px; margin-left: -1.2em; margin-top: calc(1em - 10px); border: none; }
.math { font-size: 1rem; }
.md-toc { min-height: 3.58rem; position: relative; font-size: 0.9rem; border-radius: 10px; }
.md-toc-content { position: relative; margin-left: 0px; }
.md-toc-content::after, .md-toc::after { display: none; }
.md-toc-item { display: block; color: rgb(65, 131, 196); }
.md-toc-item a { text-decoration: none; }
.md-toc-inner:hover { text-decoration: underline; }
.md-toc-inner { display: inline-block; cursor: pointer; }
.md-toc-h1 .md-toc-inner { margin-left: 0px; font-weight: 700; }
.md-toc-h2 .md-toc-inner { margin-left: 2em; }
.md-toc-h3 .md-toc-inner { margin-left: 4em; }
.md-toc-h4 .md-toc-inner { margin-left: 6em; }
.md-toc-h5 .md-toc-inner { margin-left: 8em; }
.md-toc-h6 .md-toc-inner { margin-left: 10em; }
@media screen and (max-width: 48em) {
  .md-toc-h3 .md-toc-inner { margin-left: 3.5em; }
  .md-toc-h4 .md-toc-inner { margin-left: 5em; }
  .md-toc-h5 .md-toc-inner { margin-left: 6.5em; }
  .md-toc-h6 .md-toc-inner { margin-left: 8em; }
}
a.md-toc-inner { font-size: inherit; font-style: inherit; font-weight: inherit; line-height: inherit; }
.footnote-line a:not(.reversefootnote) { color: inherit; }
.reversefootnote { font-family: ui-monospace, sans-serif; }
.md-attr { display: none; }
.md-fn-count::after { content: "."; }
code, pre, samp, tt { font-family: var(--monospace); }
kbd { margin: 0px 0.1em; padding: 0.1em 0.6em; font-size: 0.8em; color: rgb(36, 39, 41); background: rgb(255, 255, 255); border: 1px solid rgb(173, 179, 185); border-radius: 3px; box-shadow: rgba(12, 13, 14, 0.2) 0px 1px 0px, rgb(255, 255, 255) 0px 0px 0px 2px inset; white-space: nowrap; vertical-align: middle; }
.md-comment { color: rgb(162, 127, 3); opacity: 0.6; font-family: var(--monospace); }
code { text-align: left; vertical-align: initial; }
a.md-print-anchor { white-space: pre !important; border-width: initial !important; border-style: none !important; border-color: initial !important; display: inline-block !important; position: absolute !important; width: 1px !important; right: 0px !important; outline: 0px !important; background: 0px 0px !important; text-decoration: initial !important; text-shadow: initial !important; }
.os-windows.monocolor-emoji .md-emoji { font-family: "Segoe UI Symbol", sans-serif; }
.md-diagram-panel > svg { max-width: 100%; }
[lang="flow"] svg, [lang="mermaid"] svg { max-width: 100%; height: auto; }
[lang="mermaid"] .node text { font-size: 1rem; }
table tr th { border-bottom: 0px; }
video { max-width: 100%; display: block; margin: 0px auto; }
iframe { max-width: 100%; width: 100%; border: none; }
.highlight td, .highlight tr { border: 0px; }
mark { background: rgb(255, 255, 0); color: rgb(0, 0, 0); }
.md-html-inline .md-plain, .md-html-inline strong, mark .md-inline-math, mark strong { color: inherit; }
.md-expand mark .md-meta { opacity: 0.3 !important; }
mark .md-meta { color: rgb(0, 0, 0); }
@media print {
  .typora-export h1, .typora-export h2, .typora-export h3, .typora-export h4, .typora-export h5, .typora-export h6 { break-inside: avoid; }
}
.md-diagram-panel .messageText { stroke: none !important; }
.md-diagram-panel .start-state { fill: var(--node-fill); }
.md-diagram-panel .edgeLabel rect { opacity: 1 !important; }
.md-fences.md-fences-math { font-size: 1em; }
.md-fences-advanced:not(.md-focus) { padding: 0px; white-space: nowrap; border: 0px; }
.md-fences-advanced:not(.md-focus) { background: inherit; }
.typora-export-show-outline .typora-export-content { max-width: 1440px; margin: auto; display: flex; flex-direction: row; }
.typora-export-sidebar { width: 300px; font-size: 0.8rem; margin-top: 80px; margin-right: 18px; }
.typora-export-show-outline #write { --webkit-flex:2; flex: 2 1 0%; }
.typora-export-sidebar .outline-content { position: fixed; top: 0px; max-height: 100%; overflow: hidden auto; padding-bottom: 30px; padding-top: 60px; width: 300px; }
@media screen and (max-width: 1024px) {
  .typora-export-sidebar, .typora-export-sidebar .outline-content { width: 240px; }
}
@media screen and (max-width: 800px) {
  .typora-export-sidebar { display: none; }
}
.outline-content li, .outline-content ul { margin-left: 0px; margin-right: 0px; padding-left: 0px; padding-right: 0px; list-style: none; }
.outline-content ul { margin-top: 0px; margin-bottom: 0px; }
.outline-content strong { font-weight: 400; }
.outline-expander { width: 1rem; height: 1.42857rem; position: relative; display: table-cell; vertical-align: middle; cursor: pointer; padding-left: 4px; }
.outline-expander::before { content: ""; position: relative; font-family: Ionicons; display: inline-block; font-size: 8px; vertical-align: middle; }
.outline-item { padding-top: 3px; padding-bottom: 3px; cursor: pointer; }
.outline-expander:hover::before { content: ""; }
.outline-h1 > .outline-item { padding-left: 0px; }
.outline-h2 > .outline-item { padding-left: 1em; }
.outline-h3 > .outline-item { padding-left: 2em; }
.outline-h4 > .outline-item { padding-left: 3em; }
.outline-h5 > .outline-item { padding-left: 4em; }
.outline-h6 > .outline-item { padding-left: 5em; }
.outline-label { cursor: pointer; display: table-cell; vertical-align: middle; text-decoration: none; color: inherit; }
.outline-label:hover { text-decoration: underline; }
.outline-item:hover { border-color: rgb(245, 245, 245); background-color: var(--item-hover-bg-color); }
.outline-item:hover { margin-left: -28px; margin-right: -28px; border-left: 28px solid transparent; border-right: 28px solid transparent; }
.outline-item-single .outline-expander::before, .outline-item-single .outline-expander:hover::before { display: none; }
.outline-item-open > .outline-item > .outline-expander::before { content: ""; }
.outline-children { display: none; }
.info-panel-tab-wrapper { display: none; }
.outline-item-open > .outline-children { display: block; }
.typora-export .outline-item { padding-top: 1px; padding-bottom: 1px; }
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.typora-export .outline-expander::before { content: "+"; font-family: inherit; top: -1px; }
.typora-export .outline-expander:hover::before, .typora-export .outline-item-open > .outline-item > .outline-expander::before { content: "−"; }
.typora-export-collapse-outline .outline-children { display: none; }
.typora-export-collapse-outline .outline-item-open > .outline-children, .typora-export-no-collapse-outline .outline-children { display: block; }
.typora-export-no-collapse-outline .outline-expander::before { content: "" !important; }
.typora-export-show-outline .outline-item-active > .outline-item .outline-label { font-weight: 700; }
.md-inline-math-container mjx-container { zoom: 0.95; }
mjx-container { break-inside: avoid; }


.CodeMirror { height: auto; }
.CodeMirror.cm-s-inner { background: inherit; }
.CodeMirror-scroll { overflow: auto hidden; z-index: 3; }
.CodeMirror-gutter-filler, .CodeMirror-scrollbar-filler { background-color: rgb(255, 255, 255); }
.CodeMirror-gutters { border-right: 1px solid rgb(221, 221, 221); background: inherit; white-space: nowrap; }
.CodeMirror-linenumber { padding: 0px 3px 0px 5px; text-align: right; color: rgb(153, 153, 153); }
.cm-s-inner .cm-keyword { color: rgb(119, 0, 136); }
.cm-s-inner .cm-atom, .cm-s-inner.cm-atom { color: rgb(34, 17, 153); }
.cm-s-inner .cm-number { color: rgb(17, 102, 68); }
.cm-s-inner .cm-def { color: rgb(0, 0, 255); }
.cm-s-inner .cm-variable { color: rgb(0, 0, 0); }
.cm-s-inner .cm-variable-2 { color: rgb(0, 85, 170); }
.cm-s-inner .cm-variable-3 { color: rgb(0, 136, 85); }
.cm-s-inner .cm-string { color: rgb(170, 17, 17); }
.cm-s-inner .cm-property { color: rgb(0, 0, 0); }
.cm-s-inner .cm-operator { color: rgb(152, 26, 26); }
.cm-s-inner .cm-comment, .cm-s-inner.cm-comment { color: rgb(170, 85, 0); }
.cm-s-inner .cm-string-2 { color: rgb(255, 85, 0); }
.cm-s-inner .cm-meta { color: rgb(85, 85, 85); }
.cm-s-inner .cm-qualifier { color: rgb(85, 85, 85); }
.cm-s-inner .cm-builtin { color: rgb(51, 0, 170); }
.cm-s-inner .cm-bracket { color: rgb(153, 153, 119); }
.cm-s-inner .cm-tag { color: rgb(17, 119, 0); }
.cm-s-inner .cm-attribute { color: rgb(0, 0, 204); }
.cm-s-inner .cm-header, .cm-s-inner.cm-header { color: rgb(0, 0, 255); }
.cm-s-inner .cm-quote, .cm-s-inner.cm-quote { color: rgb(0, 153, 0); }
.cm-s-inner .cm-hr, .cm-s-inner.cm-hr { color: rgb(153, 153, 153); }
.cm-s-inner .cm-link, .cm-s-inner.cm-link { color: rgb(0, 0, 204); }
.cm-negative { color: rgb(221, 68, 68); }
.cm-positive { color: rgb(34, 153, 34); }
.cm-header, .cm-strong { font-weight: 700; }
.cm-del { text-decoration: line-through; }
.cm-em { font-style: italic; }
.cm-link { text-decoration: underline; }
.cm-error { color: red; }
.cm-invalidchar { color: red; }
.cm-constant { color: rgb(38, 139, 210); }
.cm-defined { color: rgb(181, 137, 0); }
div.CodeMirror span.CodeMirror-matchingbracket { color: rgb(0, 255, 0); }
div.CodeMirror span.CodeMirror-nonmatchingbracket { color: rgb(255, 34, 34); }
.cm-s-inner .CodeMirror-activeline-background { background: inherit; }
.CodeMirror { position: relative; overflow: hidden; }
.CodeMirror-scroll { height: 100%; outline: 0px; position: relative; box-sizing: content-box; background: inherit; }
.CodeMirror-sizer { position: relative; }
.CodeMirror-gutter-filler, .CodeMirror-hscrollbar, .CodeMirror-scrollbar-filler, .CodeMirror-vscrollbar { position: absolute; z-index: 6; display: none; outline: 0px; }
.CodeMirror-vscrollbar { right: 0px; top: 0px; overflow: hidden; }
.CodeMirror-hscrollbar { bottom: 0px; left: 0px; overflow: auto hidden; }
.CodeMirror-scrollbar-filler { right: 0px; bottom: 0px; }
.CodeMirror-gutter-filler { left: 0px; bottom: 0px; }
.CodeMirror-gutters { position: absolute; left: 0px; top: 0px; padding-bottom: 10px; z-index: 3; overflow-y: hidden; }
.CodeMirror-gutter { white-space: normal; height: 100%; box-sizing: content-box; padding-bottom: 30px; margin-bottom: -32px; display: inline-block; }
.CodeMirror-gutter-wrapper { position: absolute; z-index: 4; background: 0px 0px !important; border: none !important; }
.CodeMirror-gutter-background { position: absolute; top: 0px; bottom: 0px; z-index: 4; }
.CodeMirror-gutter-elt { position: absolute; cursor: default; z-index: 4; }
.CodeMirror-lines { cursor: text; }
.CodeMirror pre { border-radius: 0px; border-width: 0px; background: 0px 0px; font-family: inherit; font-size: inherit; margin: 0px; white-space: pre; overflow-wrap: normal; color: inherit; z-index: 2; position: relative; overflow: visible; }
.CodeMirror-wrap pre { overflow-wrap: break-word; white-space: pre-wrap; word-break: normal; }
.CodeMirror-code pre { border-right: 30px solid transparent; width: fit-content; }
.CodeMirror-wrap .CodeMirror-code pre { border-right: none; width: auto; }
.CodeMirror-linebackground { position: absolute; inset: 0px; z-index: 0; }
.CodeMirror-linewidget { position: relative; z-index: 2; overflow: auto; }
.CodeMirror-wrap .CodeMirror-scroll { overflow-x: hidden; }
.CodeMirror-measure { position: absolute; width: 100%; height: 0px; overflow: hidden; visibility: hidden; }
.CodeMirror-measure pre { position: static; }
.CodeMirror div.CodeMirror-cursor { position: absolute; visibility: hidden; border-right: none; width: 0px; }
.CodeMirror div.CodeMirror-cursor { visibility: hidden; }
.CodeMirror-focused div.CodeMirror-cursor { visibility: inherit; }
.cm-searching { background: rgba(255, 255, 0, 0.4); }
span.cm-underlined { text-decoration: underline; }
span.cm-strikethrough { text-decoration: line-through; }
.cm-tw-syntaxerror { color: rgb(255, 255, 255); background-color: rgb(153, 0, 0); }
.cm-tw-deleted { text-decoration: line-through; }
.cm-tw-header5 { font-weight: 700; }
.cm-tw-listitem:first-child { padding-left: 10px; }
.cm-tw-box { border-style: solid; border-right-width: 1px; border-bottom-width: 1px; border-left-width: 1px; border-color: inherit; border-top-width: 0px !important; }
.cm-tw-underline { text-decoration: underline; }
@media print {
  .CodeMirror div.CodeMirror-cursor { visibility: hidden; }
}


:root {
    --side-bar-bg-color: #fafafa;
    --control-text-color: #777;
}

@include-when-export url(https://fonts.loli.net/css?family=Open+Sans:400italic,700italic,700,400&subset=latin,latin-ext);

/* open-sans-regular - latin-ext_latin */
  /* open-sans-italic - latin-ext_latin */
    /* open-sans-700 - latin-ext_latin */
    /* open-sans-700italic - latin-ext_latin */
  html {
    font-size: 16px;
    -webkit-font-smoothing: antialiased;
}

body {
    font-family: "Open Sans","Clear Sans", "Helvetica Neue", Helvetica, Arial, 'Segoe UI Emoji', sans-serif;
    color: rgb(51, 51, 51);
    line-height: 1.6;
}

#write {
    max-width: 860px;
  	margin: 0 auto;
  	padding: 30px;
    padding-bottom: 100px;
}

@media only screen and (min-width: 1400px) {
	#write {
		max-width: 1024px;
	}
}

@media only screen and (min-width: 1800px) {
	#write {
		max-width: 1200px;
	}
}

#write > ul:first-child,
#write > ol:first-child{
    margin-top: 30px;
}

a {
    color: #4183C4;
}
h1,
h2,
h3,
h4,
h5,
h6 {
    position: relative;
    margin-top: 1rem;
    margin-bottom: 1rem;
    font-weight: bold;
    line-height: 1.4;
    cursor: text;
}
h1:hover a.anchor,
h2:hover a.anchor,
h3:hover a.anchor,
h4:hover a.anchor,
h5:hover a.anchor,
h6:hover a.anchor {
    text-decoration: none;
}
h1 tt,
h1 code {
    font-size: inherit;
}
h2 tt,
h2 code {
    font-size: inherit;
}
h3 tt,
h3 code {
    font-size: inherit;
}
h4 tt,
h4 code {
    font-size: inherit;
}
h5 tt,
h5 code {
    font-size: inherit;
}
h6 tt,
h6 code {
    font-size: inherit;
}
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</style><title>UTF-8编码及非英文字符的处理与显示</title>
</head>
<body class='typora-export os-windows'><div class='typora-export-content'>
<div id='write'  class=''><p>&nbsp;</p><p>&#8195;&#8195;<span>1个字节的存储空间，最多能表达256种不同的值。如果只表达英文字符及其标点符号，1个字节足够。但其它文字，比如中文，其“字符”有数万之多。在编码其它语言文字时，可能会使用到不同的多字节编码方案。</span></p><!--more--><p>&nbsp;</p><blockquote><p><span>版权声明</span></p><p><span>本文</span><strong><span>可以</span></strong><span>在互联网上自由转载，但必须：注明出处(作者：海洋饼干叔叔)并包含指向本页面的链接。</span></p><p><span>本文</span><strong><span>不可以</span></strong><span>以纸质出版为目的进行改编、摘抄。</span></p></blockquote><p>&nbsp;</p><h3 id='1-文本编码与解码'><span>1. 文本编码与解码</span></h3><p>&#8195;&#8195;<span>计算机是二进制的，它的文件和内存严格地说，只能存储和处理比特流，每个比特对应二进制的1位。由于这些二进制位按8位一组被分隔成字节，我们也可以认为计算机只能存储和处理字节流，用大白话说就是一个接一个的字节。</span></p><p>&#8195;&#8195;<span>所以，当我们把由多个字符构成的文章存储到计算机里的时候，存入到内存或者硬盘的并不是文字本身，而是这些文字字符的对应编码。我们以ASCII码为例为说明相关过程。ASCII码是所谓美国标准信息交换代码，它用一个字节来表示一个字符。一个字节有8位，共256种组合，用来表示英文字符、数字及标点绰绰有余。</span></p><p>&#8195;&#8195;<span>ASCII码的完整码表请见： </span><a href='http://codelearn.club/2022/05/ascii/'><span>美国信息交换标准交换代码表 - Python,C/C++ Club (codelearn.club)</span></a></p><p>&#8195;&#8195;<span>为便于讨论，我们在Windows下用记事本编辑了如下内容的文件，并保存为hw.txt。</span></p><p><img src="utf8/image-20221101165544932.png" referrerpolicy="no-referrer" alt="image-20221101165544932"></p><p>&nbsp;</p><p>&#8195;&#8195;<span>查看hw.txt的文件属性，可见该文件事实上占据了11个字节的空间。</span></p><p><img src="utf8/image-20221101165525203.png" referrerpolicy="no-referrer" alt="image-20221101165525203"></p><p>&nbsp;</p><p>&#8195;&#8195;<span>回顾hw.txt的文件内容，其中的&quot;Hello World&quot;连同其中的空格一起，正好11个字符。</span></p><p><img src="utf8/image-20221101175008387.png" referrerpolicy="no-referrer" alt="image-20221101175008387"></p><p><span>注意：000000  000013表示序号，不是文件的构成内容。</span></p><p>&nbsp;</p><p>&#8195;&#8195;<span>在Windows命令行下，使用如上图所述的od命令可以查看文件hw.txt的原始内容，其内的11个字节的值用16进制表示出来就是：</span></p><pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang=""><div class="CodeMirror cm-s-inner cm-s-null-scroll CodeMirror-wrap" lang=""><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 9.51875px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">48 65 6C 6C 6F 20 57 6F 72 6C 64</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 23px;"></div><div class="CodeMirror-gutters" style="display: none; height: 23px;"></div></div></div></pre><p>&#8195;&#8195;<span>其中，48在ASCII码里对应&#39;H&#39;，65对应&#39;e&#39;，20对应空格，64对应&#39;d&#39;... </span></p><p>&nbsp;</p><p><strong><span>文本编码</span></strong></p><p>&#8195;&#8195;<span>将文本存储至计算机内时，需要先把文本中的字符逐一转换成对应的编码，这一过程被称为”文本编码“。比如，文本&quot;Hello World&quot;被编码成字节流”48 65 6C 6C 6F 20 57 6F 72 6C 64“。 </span></p><p>&nbsp;</p><p><strong><span>文本解码</span></strong></p><p>&#8195;&#8195;<span>对于Windows记事本而言，文件hw.txt就是包含11个字节的字节流，需要将这11个字节按照码表映射至文本，再显示出来，这一过程被称为”文本解码“。比如，字节流”48 65 6C 6C 6F 20 57 6F 72 6C 64“被转换成&quot;Hello World&quot;。</span></p><p>&nbsp;</p><p><strong><span>编码方案</span></strong></p><p>&#8195;&#8195;<span>同一文字符号，在不同的编码方案内，其对应的字节或字节序列很可能不同。</span></p><ul><li><span>ASCII码使用一个字节表示一个字符，而1个字节仅有8个比特，256种组合，因此，ASCII码只能表示英文字母、数字及符号。</span></li><li><span>GB2312-80(汉语国标)使用双字节来表示一个汉字符号，同时，为了兼容英文，也用单字节来表示英文字符。理论上，GB2312-80可以较好地支持同一个文件内的中英文混合表达。但随着国际交流的日益频繁，在同一个网页或者文档里， 英、法、日、中、泰、韩等多国语言交替使用的场景屡见不鲜，此时，GB2312-80就不够用了。 后来国家又出手搞了GB18030...   但事实上未获得广泛应用。</span></li></ul><p>&#8195;&#8195;<span>为了促进世界大同，有人弄出了Unicode®，这种编码方案可以在同一文档/网页内容纳多国语言没有歧义地混合使用。</span></p><p>&nbsp;</p><h3 id='2-unicode®'><span>2. Unicode®</span></h3><p>&#8195;&#8195;<span>粗略地理解，Unicode就是一张表，这张表将世界上”所有“的文字字符，甚至一些表情符号(emoji表情)对应成互不相同的整数。Unicode®自发明以来，一直在不断修订中，以收录”新“的语言符号。至2022年9月13日止，Unicode® 15.0.0总共收录了149,186个字符。Unicode的表太长，下表给出了其中的几个示例。</span></p><center>表1 Unicode编码示例</center><figure><table><thead><tr><th><span>符号</span></th><th><span>编码（整数,16进制）</span></th><th><span>说明</span></th></tr></thead><tbody><tr><td><span>B</span></td><td><span>0042</span></td><td><span>英文字符</span></td></tr><tr><td><span>Ê</span></td><td><span>00CA</span></td><td>&nbsp;</td></tr><tr><td><span>ڣ</span></td><td><span>06A3</span></td><td><span>阿拉伯语字符</span></td></tr><tr><td><span>ॵ</span></td><td><span>0975</span></td><td><span>未知语言字符</span></td></tr><tr><td><span>ᅰ</span></td><td><span>1170</span></td><td><span>韩语符号</span></td></tr><tr><td><span>∫</span></td><td><span>222B</span></td><td><span>数学符号之积分</span></td></tr><tr><td><span>⛺</span></td><td><span>26FA</span></td><td><span>帐篷</span></td></tr><tr><td><span>ざ</span></td><td><span>3056</span></td><td><span>日语假名</span></td></tr><tr><td><span>人</span></td><td><span>4EBA</span></td><td><span>汉字</span></td></tr></tbody></table></figure><p>&nbsp;</p><h3 id='3-utf-8'><span>3. UTF-8</span></h3><p>&#8195;&#8195;<span>UTF-8可以认为是Unicode的一种实施方案，通过UTF-8可以把一个字符对应的Unicode编码（一个整数）转换成一个字节序列，这个字节序列可能包含1个、2个、3个或者4个字节。</span></p><center>表2 Unicode编码与UTF-8的转换关系</center><figure><table><thead><tr><th><span>Unicode编码（16进制）</span></th><th><span>UTF-8字节序列</span></th><th><span>说明</span></th></tr></thead><tbody><tr><td><span>000000 ~ 00007F</span></td><td><span>0xxxxxxx</span></td><td><span>单字节, 含7个x</span></td></tr><tr><td><span>000080 ~ 0007FF</span></td><td><span>110xxxxx 10xxxxxx</span></td><td><span>2字节，含11个x</span></td></tr><tr><td><span>000800 ~ 00FFFF</span></td><td><span>1110xxxx 10xxxxxx 10xxxxxx</span></td><td><span>3字节,  含16个x</span></td></tr><tr><td><span>010000 ~ 10FFFF</span></td><td><span>11110xxx 10xxxxxx 10xxxxxx 10xxxxxx</span></td><td><span>4字节,  含21个x</span></td></tr></tbody></table></figure><p>&nbsp;</p><p><strong><span>转换举例</span></strong></p><ul><li><span>对于英文字母、数字及英文符号，其Unicode编码与ASCII是一致的, 其值≤0x7F，按上表的规则，仍使用单字节编码。比如，&#39;B&#39;的Unicode编码为000042</span><sub><span>16</span></sub><span>，转换成7位二进制即为1000010</span><sub><span>2</span></sub><span>，逐一替换上表第1行中的7个x，即为01000010</span><sub><span>2</span></sub><span>，仍是42</span><sub><span>16</span></sub><span>，与&#39;B&#39;的ASCII码值完全相同。</span></li><li><span>对于阿拉伯母字符&#39;ڣ&#39;，其Unicode编码为06A3</span><sub><span>16</span></sub><span>，其值满足上表第2行的条件，按规则应使用2字节编码。06A3</span><sub><span>16</span></sub><span>转换成11位二进制即为11010100011</span><sub><span>2</span></sub><span>，逐一替代上表第2行中的11个x，即为11011010 10100011</span><sub><span>2</span></sub><span>，按16进制表达即为DA A3</span><sub><span>16</span></sub><span>。</span></li><li><span>对于汉字&#39;人&#39;，其Unicode编码为4EBA</span><sub><span>16</span></sub><span>，其值符合上表第3行的条件，按规则应使用3字节编码。4EBA</span><sub><span>16</span></sub><span>转换成16位二进制即为01001110 10111010</span><sub><span>2</span></sub><span>，逐一替代上表第3行中的16个x，即为11100100 10111010 10111010</span><sub><span>2</span></sub><span>，按16进制表达即为E4 BA BA</span><sub><span>16</span></sub><span>。</span></li></ul><p>&nbsp;</p><h3 id='3-utf-8编码示例'><span>3. UTF-8编码示例</span></h3><p>&#8195;&#8195;<span>我们使用Windows记事本编辑了一个&quot;多国语言文件&quot;，其中包含英文字母“B”，阿拉伯母字母“ڣ”，以及汉语的“人”，然后按UTF-8编码保存为文件mixed.txt。</span></p><p><img src="utf8/image-20221101203608750.png" referrerpolicy="no-referrer" alt="image-20221101203608750"></p><p>&nbsp;</p><p>&#8195;&#8195;<span>注意保存时选择UTF-8编码。</span></p><p><img src="utf8/image-20221101204117661.png" referrerpolicy="no-referrer" alt="image-20221101204117661"></p><p>&nbsp;</p><p>&#8195;&#8195;<span>查看mixed.txt文件属性，发现其尺寸为6个字节。</span></p><p><img src="utf8/image-20221101203801490.png" referrerpolicy="no-referrer" alt="image-20221101203801490"></p><p>&nbsp;</p><p>&#8195;&#8195;<span>再次使用od命令查看文件mixed.txt的原始内容，结果如下：</span></p><p><img src="utf8/image-20221101203942296.png" referrerpolicy="no-referrer" alt="image-20221101203942296"></p><p><span>注意：000000, 000006是序号信息，不是文件的构成部分。</span></p><p>&#8195;&#8195;<span>其中的&quot;42 DA A3 E4 BA BA&quot;与前述分析完全相同。编码程序完全按照上述UTF-8规则将文字&quot;Bڣ人&quot;转换为字节序列&quot;42 DA A3 E4 BA BA&quot;,然后把这个字节序列共6个字节写入文件mixed.txt。</span></p><p>&nbsp;</p><h3 id='4-utf-8的模拟解码'><span>4. UTF-8的模拟解码</span></h3><p>&#8195;&#8195;<span>当我们用记事本将文件mixed.txt中的原始内容读出时，其就是由6个字节构成的字节序列：42 DA A3 E4 BA BA</span><sub><span>16</span></sub><span>。 作为一个文字编辑软件，记事本需要通过UTF-8解码将上述字节序列查表转换成&quot;Bڣ人&quot;，然后再将其显示出来。字符的显示过程涉及绘图、字体等内容，此处略去不提。</span></p><p>&#8195;&#8195;<span>我们可以假想出记事本软件内部的解码程序的执行过程：</span></p><ul><li><span>解码程序从前至后逐一扫描字节序列，首先遇到42</span><sub><span>16</span></sub><span>，即01000010</span><sub><span>2</span></sub><span>，该字节的最高位为0，根据表2，该字节为1字节编码，其单独表示一个Unicode字符，按表2第1行的规则从中取得后7个比特，其值仍为42</span><sub><span>16</span></sub><span>，查Unicode表，即得英文字符&#39;B&#39;。</span></li><li><span>解码程序继续扫描，得DA</span><sub><span>16</span></sub><span>，即11011010</span><sub><span>2</span></sub><span>，其高3位为110，根据表2，该字节连同后面的A3合为一个2字节编码，按表2第2行的规则从中抽取11个比特，得11010100011</span><sub><span>2</span></sub><span>，即06A3</span><sub><span>16</span></sub><span>，查Unicode表，即得阿拉伯语字符‘ڣ’。</span></li><li><span>解码程序继续扫描，得E4</span><sub><span>16</span></sub><span>，即11100100</span><sub><span>2</span></sub><span>，其高4位为1110，根据表2，该字节连同后面的BA BA合为一个3字节编码，按表2第3行的规则从中抽取16个比特，得01001110 10111010</span><sub><span>2</span></sub><span>，即4EBA</span><sub><span>16</span></sub><span>，查Unicode表，即得汉字&#39;人&#39;。</span></li><li><span>字节序列结束，解码程序终止。</span></li></ul><p>&nbsp;</p><p>&#8195;&#8195;<span>从上述解码过程，读者不难看出，UTF-8的编码是没有歧义的，即特定的字节序列与特定的文本内容一一对应。在以汉字为主的文档里，使用UTF-8编码，一个汉字需要3个字节来表达，而使用GB2312-80，一个汉字只需要2个字节来表达。相较于后者，UTF-8编码的文档需要占据更多的存储空间以及网络带宽。</span></p><p>&nbsp;</p><h3 id='5-utf-16-utf-32'><span>5. UTF-16, UTF-32</span></h3><p>&#8195;&#8195;<span>作者觉得没什么意思，UTF-8现在是主流，读者在安装Linux，设计网页时，如果选用UTF-8编码，是最安全的。</span></p><p>&#8195;&#8195;<span>事实上，除了UTF-8，GB2312-80，ASCII，世界还有很多很多乱七八糟的编码方案...   </span></p><p>&nbsp;</p><h3 id='6-为什么会乱码'><span>6. 为什么会乱码</span></h3><p><img src="utf8/image-20200216161744112.png" referrerpolicy="no-referrer" alt="image-20200216161744112"></p><p>&#8195;&#8195;<span>读者或许在程序开发的过程中看到过如上图所示的乱码现象。所谓乱码，本质是文本编码与文本解码发生了错位，如果把一个GB2312-80编码的文档按照UTF-8来进行解码，自然会发生错误，形成所谓“乱码”。</span></p></div></div>
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